This invention relates to upgrading of hydrocarbon feed materials by catalytic hydrotreating. More particularly, the invention relates to an improved catalyst and process for hydrodemetallation of heavy hydrocarbons.
Decreasing supplies of high quality crude oils have focused considerable attention on refining lower quality feeds in recent years. Among such materials are those such as medium and heavy petroleum distillate fractions, crude oil resids, whole shale oils, tar sand oils and fractions thereof that require upgrading, for example, from the standpoint of removing or reducing the content of sulfur, nitrogen and/or metals, to facilitate conversion to more useful products. Catalytic hydrotreating is a well known means for upgrading feeds in need thereof. Typically, a feed is contacted with hydrogen in the presence of catalyst under conditions that vary somewhat depending on factors such as the particular feed to be upgraded, the type of process being operated, reaction zone capacity and other factors known to persons skilled in the art.
In terms of general composition, hydrotreating catalysts typically comprise a hydrogenating component and a porous, refractory inorganic oxide support. Physical properties that are important from the standpoint of demetallation activity include surface area, pore volume and pore size distribution. General guidelines with respect to catalysts suitable for demetallation use are disclosed in U.S. Pat. No. 3,180,820 (Gleim et al.). In terms of composition, the catalysts of Gleim et al. comprise a metallic component having hydrogenating activity, e.g., a Group V, VI, iron group or platinum group metal component, composited with a refractory inorganic oxide having surface areas and pore volumes that can vary over wide ranges. Catalyst physical properties include surface areas of about 50-700 m.sup.2 /g, pore diameters of about 20-600 .ANG. and pore volumes of 0.1-20 cc/g.
Lacking from the generalized teaching of Gleim et al. is a consideration of the interrelationships between and among physical properties and the effects thereof on catalyst performance. For example, the desirability of maximizing catalyst surface area and pore volume in order to provide high exposure of feed components to catalytically active sites, and thus, maximum activity, is well known. At the same time, however, if surface area and pore volume are too high, bulk density and mechanical strength of a catalyst can decrease to the point that use of the catalyst in hydrotreating processes is impractical or even impossible despite high activity. For example, in expanded bed processes, bulk density must be high enough to avoid substantial carryover of catalyst particles though not so high as to require unreasonably high space velocities to ensure adequate bed expansion. Of course in both expanded and fixed bed operations, it is desirable to maximize bulk density to the extent consistent with the aforesaid considerations in order to maximize catalyst loading and thereby maintain high productivity. Mechanical strength of catalyst particles is important from the standpoint of fixed bed use in that particles must be capable of withstanding the pressure drop through the bed. In expanded bed operations pressure drop through the catalyst bed is lower than in fixed bed processes; however, if catalyst particles do not exhibit sufficient crush strength and abrasion resistance collisions with each other and reactor internals can lead to excessive fragmentation of the particles and inferior performance.
Pore size distribution also influences both catalytic activity and suitability for process use. Subject to the aforesaid considerations with respect to bulk density and crush strength, it is desirable to provide catalyst particles having a high level of small or intermediate-sized pores because, for a given total pore volume, distribution thereof in many smaller pores gives higher surface area than distribution in a smaller number of larger pores. While smaller pores are thus desirable from the standpoint of maximizing surface area, such pores also are more susceptible to plugging than larger pores, and thus, if too many pores of too small size are present, demetallation activity often declines substantially during process use. If activity declines too rapidly, losses in productivity and/or increases in catalyst replacement costs are incurred.
From the foregoing, it can be appreciated that a balance must be struck between and among catalyst physical properties to ensure a desirable combination of activity, activity maintenance and suitability for process use. It is an object of this invention to provide a catalyst having such a desirable balance of properties. A further object of the invention is to provide an improved hydrotreating process using such catalyst. A more specific object is to provide an improved process for upgrading hydrocarbon feeds susceptible to upgrading in terms of reduction in metals content. Another object of the invention is to provide a catalyst useful for demetallation and desulfurization of hydrocarbon feeds containing high levels of contaminants. A further object is to provide an overall process for upgrading hydrocarbon feeds in need of upgrading wherein demetallation is conducted in the presence of the invented catalysts in a first zone and further hydrotreating is carried on in one or more subsequent zones with one or more other catalysts. Other objects of the invention will be apparent to persons skilled in the art from the following description and the appended claims.
We have now found that the objects of this invention can be attained by the provision of catalysts having a specific combination of surface area, pore volume, pore size distribution and bulk density tailored to provide high hydrotreating activity and exceptional activity maintenance along with a high degree of flexibility in terms of suitability for process use. In greater detail, the catalysts of this invention have moderate-to-high surface areas and pore volumes which, in conjunction with bimodal distribution of pore sizes and concentration of micropore volume in pores large enough to accommodate metals-containing components of hydrocarbon feeds, contribute to the superior activity and activity maintenance properties of the catalyst. In fact, the invented catalysts have the capacity to continue removing metals at metals loadings as high as 150-200% based upon catalyst weight. Further, depending on the choice of hydrogenating component, the catalysts can exhibit substantial desulfurization activity in addition to demetallation activity. Bulk density varies over a relatively narrow range which, at its upper end, is well suited for fixed bed use, while at its lower end, is well suited for expanded bed use. Throughout the range, bulk density is high enough to ensure economically acceptable catalyst loadings.
While not wishing to be bound by theory, it can be speculated that the physical properties of the invented catalysts are critical from the standpoint of demetallation performance in that the bimodal distribution of pores provides a high micropore volume that contributes to a surface area great enough to provide a high population of active sites available for catalyzing the reactions involved in demetallation, desulfurization and so forth. Concentration of micropore volume in pores large enough to accommodate metals-containing components of hydrocarbon feeds contributes to activity and maintenance of activity in that a high level of sites is provided in pores to which metals-containing components have access and plugging of pores is minimized. The bimodal pore size distribution of the invented catalysts also provides an appreciable level of macropores which serve as low surface area channels throughout the catalyst particles which facilitate rapid diffusion of reactants into the smaller pores where demetallation reactions occur. It can be theorized that without the macropore network, metal sulfides and/or coke would deposit rapidly in the smaller pores near the external surface of the catalyst particles. This, in turn, would result in pore mouth plugging and catalyst deactivation. The low surface area of the macropores of the invented catalysts limits the concentration of active sites to which reactants are exposed during passage through the macropore network such that reaction in macropores is limited and access to the smaller high surface area pores is maintained.
Proposals that may be of interest with respect to the present invention in disclosing attempts to provide hydrotreating catalysts having specific combinations of physical properties include U.S. Pat. No. 3,887,455 (Hamner et al.) which discloses particulate solids of "critical pre-selected pore size distribution, extremely low density, and ultra high porosity" for use in denitrogenation, desulfurization and demetallation of heavy crudes and resids, which particulate solids stratify during use in ebullated bed processes due to deposition of metals and/or coke so as to facilitate removal of spent solids. The particulate solids may be a catalyst comprising a hydrogenating component supported on an inorganic oxide. The particulate solids have at least about 50% of total pore volume in pores having radii of about 50 to about 150 .ANG., less than 20% of pore volume in pores having radii of 0-50 .ANG., surface area of at least about 200-600 m.sup.2 /g and total pore volume of 0.8-3.0 cc/g. Catalyst density ranges from 0.25-0.7 g/cc depending largely on hydrogenating metal content. Example 1 of Hamner et al. illustrates stratification of a mixture of alumina pellets with catalysts having properties within the aforesaid ranges although no denitrogenation, desulfurization or demetallation results are reported. Examples 2 and 3 simulate use of the patentee's catalysts to reduce metals content of a heavy hydrocarbon feed from 480 ppm to 50 ppm in a first stage and from 50 ppm to less than 5 ppm in a second stage. Hamner et al. fails to disclose or suggest either the surface area or bimodal pore size distribution of the invented catalysts.
U.S. Pat. No. 3,876,523 (Rosinski et al.) discloses hydrodemetallation-hydrodesulfurization catalysts comprising a hydrogenating component composited with a refractory support and having a bimodal distribution of pores such that not less than 60% of pore volume is in pores of 50-100 .ANG. radius and not less than about 5% of pore volume is in pores greater than 250 .ANG. radius. Unlike the invented catalysts, those according to Rosinski et al. have surface areas of 40-150 m.sup.2 /g, preferably less than 110 m.sup.2 /g. Catalysts similar to those of Rosinski et al. are disclosed in U.S. Pat. No. 4,016,067 (Fischer et al.) and U.S. Pat. No. 4,082,695 (Rosinski et al.).
U.S. Pat. No. 3,898,155 (Wilson) discloses simultaneous demetallation and desulfurization of heavy oils using catalysts comprising a Group VIB metal and at least one Group VIII metal composited with an alumina support, such catalysts having a bimodal distribution of pores such that macropore (&gt;300 .ANG. pore radius) volume is 10-40% of total pore volume, micropore (0-300 .ANG. pore radius) volume is 60-90% of total pore volume and at least 80% of such micropore volume is in pores having radii of at least 50 .ANG.. According to Wilson's broad teaching, the disclosed catalysts have surface areas of at least 100 m.sup.2 /g, total pore volumes of at least 0.5 cc/g and average pore diameters of at least 100 .ANG. calculated as 4 V/A. However, the highest total pore volume reported in the patentee's examples is 0.879 cc/g. In contrast, total pore volume of the invented catalysts is at least 0.9 cc/g and typical micropore (radii up to 600 .ANG.) volume of the invented catalysts is greater than Wilson's total pore volume, though it is noted that a portion of Wilson's macropore radius range falls within the micropore range of the invented catalysts. Further, Wilson fails to disclose or suggest the invented catalysts' combination of surface area and bulk density.
U.S. Pat. No. 4,102,822 (Mulaskey) discloses hydrotreating catalysts comprising a rigidly interconnected pack of irregularly shaped particles of specified sizes. There is a bimodal distribution of pores in the pack, with access pores of 500-75,000 .ANG. radii contributing at least about 3% of pore volume. Surface area of the disclosed catalysts ranges from 0.1 to above 500 m.sup.2 /g, with 120-200 m.sup.2 /g being preferred. The patentee also teaches that the catalysts have total pore volume of 0.6 cc/g with about 68% thereof being in the form of micropores (&lt;500 .ANG.) and about 32% being in the form of interconnected, access macropores. Column 4 lines 33-38. The patentee fails to disclose or suggest either the total pore volume or pore size distribution of the invented catalysts.
Other proposals that may be of interest in disclosing demetallation catalysts having specific combinations of physical properties are summarized in Table 1 wherein "SA" stands for surface area, "PV" stands for pore volume and "PSD" stands for pore size distribution.
TABLE 1 __________________________________________________________________________ U.S. PAT. NO. SA PV PSD (INVENTOR) (m.sup.2 /g) (cc/g) PV PORE RADIUS (.ANG.) __________________________________________________________________________ "minimal" 3,977,961 Approximately 0.8-3.0 Approximately 0-25 (Hamner) .gtoreq.200-600 50-100 3,998,722 Approximately 0.8-3.0 Approximately 75-125 (Mayer et al.) .gtoreq.200-600 .gtoreq.15.sup.(2) 4,014,821 Approximately 0.8-3.0 Approximately 87.5-137.5 (Hamner) .gtoreq.200-600 .gtoreq.15.sup.(3) "minimal" 150-175 4,003,828.sup.(4) 172-292.sup.(5) 0.41-0.56.sup.(5) UNSPECIFIED (Eberly, Jr.) 4,089,774 125-210 0.4-0.65 .gtoreq.10 &lt;15 (Oleck et al). .gtoreq.45 15-75 .gtoreq.15 &gt;150 4,119,531 .gtoreq.120 .gtoreq.0.7 UNSPECIFIED (Hopkins et al.) 4,192,736.sup.(4) UNSPECIFIED 0.3-1.1 .gtoreq.50 30-125 (Kluksdahl) .gtoreq.3 &gt;500 4,225,421 140-300 0.4-1.0 3-30 .gtoreq. 300 (Hensley, Jr. et al.) 97-70 &lt;300 60-95% 25-100 of PV in R &lt; 300 0-15% 100-300 of PV in R &gt; 300 4,242,236 150-300 0.75-1.3 &lt;10 .gtoreq.500 (Blakely) 0-15% 100-300 of PV in R &lt; 300 __________________________________________________________________________ .sup.(1) Catalyst of average particle diameter up to 1/50". .sup.(2) Catalyst of average particle diameter of 1/50-1/25". .sup.(3) Catalyst of average particle diameter of 1/25-1/8". .sup.(4) Catalysts contain phosphatedalumina supports. .sup.(5) Values taken from patentee's examples.
Other proposals of possible interest from the standpoint of disclosing catalysts having specific combinations of properties, though lacking in reported demetallation activity as well as distinguishable in terms of physical properties are summarized in TABLE 2.
TABLE 2 ______________________________________ PSD PORE U.S. PAT. NO. SA PV RADIUS (INVENTOR) (m.sup.2 g) (cc/g) PV (.ANG.) ______________________________________ 3,622,500.sup.(1) UN- 0.4- 0.3- &lt;125 (Alpert et SPECI- 1.1 0.5 cc/g al.) FIED 3,870,623 UN- 0.4- 0.1- &gt;125 (Johnson et SPECI- 1.1 0.6 cc/g al.) FIED 3,803,027.sup.(2) .gtoreq.100 0.41- 0.4- 7-300 (Christman et 0.58.sup.(3) 0.8 cc/g al.) 3,843,509.sup.(4) 181- 0.43- .gtoreq.50% 50-300 (Suto et al.) 283.sup.(3) 0.57.sup.(3) .gtoreq.0.30 cc/g 0-300 Approximately &lt;25% of 0-30 PV in R = 0-300 Approximately &lt;40% of 75-300 PV in R = 0-300 Approximately &lt;0.25 cc/g 75- 75,000 3,966,588.sup.(5) 225-400 1.0- &gt;50% &lt;500 (Beaty, Jr.) 2.75 4,008,149.sup.(6) 250-300 0.5- Approximately 30-75 (Itoh et al.) 1.0 .gtoreq.80% of PV in R = 0-75 &lt;20% of 75-150 PV in R = 0-150 0.45- 0-300 0.6 cc/g &lt;0.1 cc/g 75-500 4,051,021 150-450 0.3-1.0 .gtoreq.50% 35-80 (Hamner) 4,066,572.sup.(7) 62-311 0.51-1.1 6-60% &lt;50 (Choca) ______________________________________ .sup.(1) Bulk density = 0.4-1.0 g/cc. .sup.(2) Bulk density = 0.3-0.8 g/cc and Specific Volume of Pores (define as density .times. volume in pores with radii of 7-300 .ANG. .times. volume % of PV in pores with radii of 50-300 .ANG.) .gtoreq. 20. .sup.(3) Values taken from patentee's examples. .sup.(4) Examples report bulk density = 0.6-0.81 g/cc. .sup.(5) Loose bulk density = 7.5-25 lb/ft.sup. 3 = 0.12-0.40 g/cc. .sup.(6) Bulk density = 0.5-1.0 g/cc. .sup.(7) Phosphatedalumina support. All values taken from patentee's examples.
As will be apparent from the following description, none of the patents discussed hereinabove and summarized in TABLES 1 and 2 discloses or suggests the novel combination of physical properties that we have found to yield the superior hydrotreating results, especially in terms of demetallation, that are attained according to the present invention.